This invention relates to a cylinder recognition apparatus which can recognize a prescribed reference cylinder of an internal combustion engine as well as generate control signals for controlling the ignition timing of the engine.
In order for an internal combustion engine to operate optimally, fuel injection and ignition must take place at prescribed rotational angles of the crankshaft of the engine, i.e., when each piston of the engine is at a prescribed position with respect to top dead center. For this reason, an engine is equipped with a rotational position sensor which senses the rotational angle of the crankshaft of the engine. One common type of position sensor is in the form of a rotating plate mounted on a rotating shaft (such as the distributor shaft) which rotates in synchrony with the crankshaft of the engine. The rotating plate has a set of slits formed in it at prescribed locations. A light emitting diode is disposed on one side of the rotating plate, and a light sensor is disposed on the other side of the rotating plate in alignment with the light emitting diode. The light sensor generates an output signal each time one of the slits passes between the light sensor and the light emitting diode. The slits, which are equal in number to the cylinders, are disposed so as to correspond to prescribed rotational angles of the crankshaft and thus to prescribed positions of each piston with respect to top dead center.
In addition to knowing when the crankshaft reaches a prescribed rotational position for each cylinder, in engines in which the cylinders are individually controlled, it is necessary to be able to identify each cylinder. Engines which perform individual control of the cylinders are therefore equipped with a second position sensor for sensing when the crankshaft rotational angle is such that the piston of a specific reference cylinder is in a prescribed position. The second position sensor frequently comprises an additional slit which is formed in the above-described rotating plate, an additional light emitting diode, and an additional light sensor which detects the passage of light through the additional slit as the rotating plate is rotated. By using the outputs of the two position sensors in conjunction, it can be determined which cylinder of the engine is firing at any given time.
Thus, a conventional engine is frequently equipped with two position sensors, each including a light emitting diode and a light sensor. However, as position sensors are expensive and each one requires a separate interface circuit for connection to an engine controller, the use of two separate position sensors is uneconomical. It is also disadvantageous from the standpoint of space utilization in an engine.